1. Field of the Invention
The present invention relates generally &to a multilayer capacitor utilizing a sintered body obtained by laminating and cofiring a plurality of ceramic green sheets with electrode materials interposed therebetween and more particularly, to a multilayer capacitor suitable for the use as a noise filter or the like.
2. Description of the Background Art
Referring to FIGS. 1 to 3, description is made of an example of a multilayer capacitor heretofore used as a noise filter.
As shown in an exploded perspective view of FIG. 1, this multilayer capacitor is constructed by using a
body obtained by laminating a and cofiring plurality of ceramic green sheets mainly composed of dielectric materials. More specifically, on a rectangular ceramic green sheet 1, an inner electrode 2 having a smaller Width than that of the ceramic green sheet 1 is formed so as to extend between both edges 1a and 1b. On the o&her hand, a plurality of second inner electrodes 4 to 7 are formed on the upper surface of a ceramic green sheet 3 so as to extend between longitudinal edges 3a and 3b. The above-described inner electrodes 2 and 4 to 7, which are formed by applying and printing conductive pastes on the ceramic green sheets 1 and 3, are completed by sintering the ceramic green sheets in a sintering process as described below.
A plurality of ceramic green sheets 1 and 3 are alternately laminated; an adequate number of ceramic green sheets 8 being free of an electrode on its upper surface are further laminated in the uppermost part (also in the lowest part, if necessary); and the ceramic green sheets 1, 3 and 8 are sintered after applying pressure in the direction of the thickness, thereby to obtain a sintered body.
As shown in FIG. 2 by imaginary lines outer electrodes 9, 10, 11a to 14a and 11b to 14b are formed on external side surfaces of the above described sintered body. More specifically, the pair of outer electrodes 9 and 10 is formed so as to be electrically connected to both ends of the above-described first inner electrode 2. In addition, the pair of outer electrodes 11a and 11b is formed so as to be electrically connected to both ends of the plurality of first inner electrodes 4. Similarly, the pairs of outer electrodes 12a and 12b to 14a and 14b are respectively formed so as to be electrically connected to both ends of the other inner laminated electrodes 5 to 7, respectively.
Accordingly, the following becomes apparent. In the above-described multilayer capacitor, a three-terminal type circuit shown in FIG. 3 is constituted between the pair of outer electrodes 11a and 11b and the outer electrode 9 or 10. Similarly, the circuit shown in FIG. 3 is respectively constituted between the other pairs of outer electrodes 12a and 12b, 13a and 13b and 14a and 14b and the outer electrode 9 or 10. More specifically, four noise filter units using the three terminal type circuit shown in FIG. 3 are constituted in this multilayer capacitor.
Meanwhile, in the above-described multilayer capacitor, filter characteristics can be improved by increasing capacitance between the first inner electrode 2 and each of the second inner electrodes 4 to ? in the noise filter units. Accordingly, the first inner electrode 2 is generally formed so as to have a relatively large width over almost the entire upper surface of the ceramic green sheet 1 (FIG. 1). Therefore, the upper surface of the ceramic green sheet 1 is only exposed in very narrow regions outside of side edges 2a and 2b of the first inner electrode 2. As a result, the ceramic green sheet 1 and the ceramic green sheet 3 laminated thereon are joined to each other only in regions with a small area there the upper surface of the ceramic green sheet I is exposed. Thus, the joining force between the ceramic green sheets 1 and 3 is weak. Consequently, delamination caused by the shrinkage or the like at the time of sintering is liable to occur, resulting in the possibility degrading filter characteristics.
Furthermore, when the width of the first inner electrode 2 ia made smaller, the area of the regions where the upper surface of the above-described ceramic green sheet is exposed can be increased, thereby hindering delamination. In such a case, however, relatively wide portions of the second inner electrodes 4 to 7 are forced out of the side edges 2a and 2b of the first inner electrode 2, resulting in the possibility of causing crosstalk due to stray capacitance between adjacent ones of the second inner electrodes 4 to 7.
Additionally, the above-described multilayer capacitor has the disadvantage in that realization cannot be made of good insertion loss characteristics, because the equivalent circuit shown in FIG. 3 is formed only of capacitor components.